Until about the early 1970's, virtually all golf balls in the modern era had their dimple layout based on an octahedron projected onto the surface of the golf ball. An octahedron is an eight-sided figure which, when projected onto a golf ball surface, divides the surface into eight equal spherical triangular sections. If the dimples on the golf ball are confined in these eight sections, as was the practice in the golf industry, the golf ball has three "parting lines," i.e. great circles which pass about the golf ball and are not intersected by any dimples.
The term "parting line" emanates from the fact that spherical objects, such as golf balls, must be made in multi-piece molds. Golf balls are typically made in two hemispherical molds, by either compression or injection molding. No matter which type of molding is used, there is a junction between the two molds at which "flash" forms. When the molds are parted, this flash is called the "parting line." The flash is typically buffed off so that the parting line becomes essentially invisible. It will be appreciated, however, that, since a dimple is a depression in the surface of the golf ball, it is very difficult, if not impossible, to buff the flash out of a dimple without destroying the land area between adjacent dimples. Therefore, golf ball makers virtually always make the parting line free of dimples. As discussed hereinafter, some golf balls, either for aerodynamic or aesthetic reasons, have more than one great circle path which is not intersected by any dimples. Any one of the great circle paths not intersected by dimples can be the actual mold parting line. However, as used herein, the term "parting line" means any great circle path which is not intersected by any dimples, i.e. the term "parting line" as used herein is not limited to the flash line created by the hemispherical molds used to form a golf ball.
In a golf ball derived from an octahedron, there are three parting lines and the three parting lines cross each other at right angles; as a result, the included angle of the corners of each of the eight spherical triangles of an octahedron projected onto a golf ball is a right angle. It will be appreciated that, while the three included angles of a two-dimensional triangle will always total exactly 180.degree., the three included angles of a spherical triangle, i.e. a triangle on the surface of a sphere, will always exceed 180.degree. and, with the octahedron layout, will total 270.degree..
The planar/spherical relationship holds true for other geometric shapes, e.g. squares, pentagons, hexagons, etc. While, for example, a planar square will always total 360.degree., a spherical square will always exceed 360.degree.. Since the present invention relates to golf balls, which are spheres, it will be understood that where a term such as "square", "triangle", or the like is used when referring to the surface of the golf ball, it always means the spherical square, spherical triangle, etc.
In the early 1970's, some golf ball manufacturers moved away from the octahedron as the basic pattern and adopted the icosahedron, a layout which has one parting line. In ensuing years, others have adopted and modified the icosahedron layout on the surface of a golf ball to obtain different dimple arrangements. U.S. patents which use the icosahedron as the basis for the dimple arrangement include, for example, U.S. Pat. Nos. 4,560,168; 4,844,472; 4,880,241; 4,925,193; 4,936,587; and 5,009,427.
Other geometric patterns besides the icosahedron have also been used for arranging the dimples on the surface of the golf ball, primarily to create more parting lines. The primary advantages of having more than one parting line are aerodynamics and aesthetics. With respect to aerodynamics, the United States Golf Association (USGA) adopted a rule in the early 1980's that requires that a golf ball "perform in general as if it were spherically symmetrical." The USGA set up testing procedures at its facilities in Far Hills, New Jersey, to ensure that golf balls met this spherical symmetry standard. Some of the golf balls with an icosahedron layout, which had a single parting line and uniformly shaped dimples, did not pass the USGA symmetry tests and were, therefore, not on the USGA list of Conforming Golf Balls. Since virtually all golfers, including professional, amateur and hacker, will only play with golf balls approved by the USGA, failure of a golf ball to be on the USGA list of Conforming Golf Balls is a golf ball's kiss of death. Golf balls having multiple parting lines are generally spherically symmetrical and, to the best of the knowledge of the applicant, no golf ball with three or more parting lines and uniformly shaped dimples has ever failed to pass the USGA spherical symmetry test.
With respect to the aesthetic aspect, a single parting line can be a distraction to a golfer, especially if it has writing such as a trademark thereon. As is known, golfers tend to be very intense when striking a golf ball. By having multiple parting lines, the distraction of a single band around the ball is eliminated.
It will be appreciated, of course, that golf balls can be made with a single parting line which will pass the USGA spherical symmetry test. Such balls can be made with the parting line substantially inconspicuous if the trademarks or other indicia are applied randomly rather than on the parting line.
One of the more popular of the other geometric patterns has been the cube. U.S. patents which arrange dimples on the surface of a golf ball on the basis of a cube or a modification of a cube or derivation from a cube include U.S. Pat. Nos. 4,772,026; 4,971,330; 4,973,057; 4,974,853; 4,974,855; 4,974,856; and 4,982,964.
There have also been various other geometric shapes which have been used for arranging the dimples on the surface of a golf ball. Among these are the cuboctahedron, U.S. Pat. No. 4,762,326; modified octahedron, U.S. Pat. No. 4,948,143; truncated octahedron, U.S. Pat. No. 4,765,626; hexaoctahedron, U.S. Pat. No. 4,974,854; decahedron, U.S. Pat. No. 4,998,733; and dodecahedron, U.S. Pat. No. 4,877,252.
In addition to those patents which arrange dimples on the surface of a golf ball according to a polyhedron, there are also U.S. patents which use combinations of various geometric shapes but without drawing the dimple arrangement from a specific polyhedron. For example, U.S. Pat. No. 4,886,277 arranges six squares and eight hexagons on the surface of a golf ball and arranges the dimples according to the layout of the squares and hexagons. U.S. Pat. No. 5,046,742 is similar to the foregoing patent except that it uses twelve pentagons and twenty hexagons to establish the dimple arrangement. Similarly, U.S. Pat. No. 4,932,664 uses two pentagons, ten trapezoids and ten triangles.
A number of the foregoing patents teach that the dimples can be arranged on the surface of the golf ball so that there are a plurality of parting lines, i.e. great circle paths which are not intersected by any dimples. As described in the prior art, the number of parting lines which can be obtained with basic geometric arrangements includes: one, U.S. Pat. Nos. 4,813,677; 4,915,390; 4,925,193; 4,932,664; three, U.S. Pat. Nos. 4,720,111; 4,765,626; 4,946,167; 5,009,428; 5,033,750; four, U.S. Pat. Nos. 4,886,277; 4,948,143; 4,973,057; 4,979,747; six, U.S. Pat. Nos. 4,560,168; 4,772,026; 4,982,964; seven, U.S. Pat. Nos. 4,762,326; 4,869,512; 4,974,856; nine, U.S. Pat. Nos. 4,869,512 and 4,974,855; ten, U.S. Pat. No. 4,971,330; twelve, U.S. Pat. No. 4,974,854; thirteen, U.S. Pat. No. 4,974,853; fifteen, U.S. Pat. No. 4,844,472; twenty-one, U.S. Pat. No. 4,867,459; twenty-five, U.S. Pat. No. 4,867,459; and thirty-one, U.S. Pat. No. 4,867,459. While these many different types of possible parting lines are disclosed, some of the patents also teach that dimples can intersect one or more of the parting lines, see for example U.S. Pat. Nos. 4,974,856 and 4,982,964. Indeed, one patent, U.S. Pat. No. 4,915,389, requires that all dimples intersect great circle paths on the surface of the golf ball.